@Katy5 It's not a glitch. There are two types of communications from guests:
A reservation Inquiry and a Reservation Request. What's the difference? Read this help article:
https://community.airbnb.com/t5/Tips-Tricks/Reservation-Inquiry-or-Request-What-s-the-Difference-A-C...
If your guest sent you an Inquiry, your options are to Pre-approve, Decline, Respond, or Dismiss.
If your guest sent you a reservation request, your options are to Accept or Decline. You cannot send a Pre-Approval as a response to a reservation request.
Sounds like your guest might have sent you an inquiry which you then Pre-Approved and instead of accepting the Pre-Approval, sent you a Reservation Request. Not understanding, you probably didn't realize that you had to Accept or Decline the reservation request while you were waiting for a response to your Pre-Approval. Confusion on both ends, I'm afraid!